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<h2 id="%E5%87%BD%E6%95%B0%E5%BC%8F%E7%BC%96%E7%A8%8B">函数式编程</h2>
<h2 id="1%E4%BB%80%E4%B9%88%E6%98%AF%E5%87%BD%E6%95%B0%E5%BC%8F%E7%BC%96%E7%A8%8B%E5%AE%83%E5%92%8C%E9%9D%A2%E5%90%91%E5%AF%B9%E8%B1%A1%E5%92%8C%E9%9D%A2%E5%90%91%E8%BF%87%E7%A8%8B%E6%9C%89%E4%BB%80%E4%B9%88%E5%8C%BA%E5%88%AB%E4%BC%98%E5%8A%BF">1.什么是函数式编程，它和面向对象和面向过程有什么区别（优势）</h2>
<ul>
<li>函数式编程是面向函数编程：对于运算过程的抽象。</li>
<li>理解：比起面向过程，函数式编程像是把过程封装成一个管道（映射关系），创建自己的API工具箱。不同于面向对象的是，面向对象是从大到小，类到对象更关注的是属性。而函数式编程是由小到大，将多个基本方法组装成高阶函数。js的方法是对象，但是函数式编程更关注的是逻辑封装而不是属性继承</li>
</ul>
<h2 id="2%E6%88%91%E4%BB%AC%E8%83%BD%E7%94%A8%E5%AE%83%E5%81%9A%E4%BB%80%E4%B9%88">2.我们能用它做什么</h2>
<ul>
<li>1)屏蔽细节：只关注结果封装过程（形比于管道）
函数式编程，重要的是数据之间的映射关系（数据处理），保证相同输入能够有相同输出（所以函数式编程要避免硬编码情况出现，不然会污染管道，不能保证管道的通用性）</li>
<li>2)怎么用：高阶函数可以自己定义
es6给我们提供了大量的高阶函数：forEach,filter,some,every,map
我们可以定义自己的高阶函数，用于项目场景：数据格式化(时间格式，表单清除脏数据)</li>
</ul>
<pre class="hljs"><code><div><span class="hljs-comment">// 对象value值去空字符串</span>
<span class="hljs-keyword">const</span> removeEmpty = <span class="hljs-function">(<span class="hljs-params">obj</span>) =&gt;</span> {
  <span class="hljs-keyword">const</span> thatObj = <span class="hljs-built_in">JSON</span>.parse(<span class="hljs-built_in">JSON</span>.stringify(obj))
  <span class="hljs-keyword">const</span> keys = <span class="hljs-built_in">Object</span>.keys(thatObj)
  keys.some(<span class="hljs-function">(<span class="hljs-params">item</span>) =&gt;</span> {
    <span class="hljs-keyword">if</span> (<span class="hljs-keyword">typeof</span> thatObj[item] === <span class="hljs-string">'string'</span> &amp;&amp; item.toUpperCase().indexOf(<span class="hljs-string">'TIME'</span>) === <span class="hljs-number">-1</span>) {
      thatObj[item] = thatObj[item].replace(<span class="hljs-regexp">/\s/g</span>, <span class="hljs-string">''</span>)
    }
  })
  <span class="hljs-keyword">return</span> thatObj
}
<span class="hljs-comment">// 对象去除含空的key</span>
<span class="hljs-keyword">const</span> removeKey = <span class="hljs-function">(<span class="hljs-params">obj</span>) =&gt;</span> {
  <span class="hljs-keyword">const</span> thatObj = removeEmpty(obj)
  <span class="hljs-keyword">const</span> keys = <span class="hljs-built_in">Object</span>.keys(thatObj)
  keys.some(<span class="hljs-function">(<span class="hljs-params">item</span>) =&gt;</span> {
    <span class="hljs-keyword">if</span> (thatObj[item] === <span class="hljs-string">''</span>) {
      <span class="hljs-keyword">delete</span> thatObj[item]
    }
  })
  <span class="hljs-keyword">return</span> thatObj
}
<span class="hljs-comment">// UTC时间格式转换</span>
<span class="hljs-keyword">const</span> formatUTC = <span class="hljs-function">(<span class="hljs-params">utcDatetime</span>) =&gt;</span> {
  <span class="hljs-comment">// 转为正常的时间格式 年-月-日 时:分:秒</span>
  <span class="hljs-keyword">const</span> Tpos = utcDatetime.indexOf(<span class="hljs-string">'T'</span>)
  <span class="hljs-keyword">const</span> Zpos = utcDatetime.indexOf(<span class="hljs-string">'Z'</span>)
  <span class="hljs-keyword">const</span> yearMonthDay = utcDatetime.substr(<span class="hljs-number">0</span>, Tpos)
  <span class="hljs-keyword">const</span> hourMinuteSecond = utcDatetime.substr(Tpos + <span class="hljs-number">1</span>, Zpos - Tpos - <span class="hljs-number">1</span>)
  <span class="hljs-keyword">const</span> newDatetime = <span class="hljs-string">`<span class="hljs-subst">${yearMonthDay}</span> <span class="hljs-subst">${hourMinuteSecond}</span>`</span> <span class="hljs-comment">// 2017-03-31 08:02:06</span>

  <span class="hljs-comment">// 处理成为时间戳</span>
  <span class="hljs-keyword">let</span> timestamp = <span class="hljs-keyword">new</span> <span class="hljs-built_in">Date</span>(<span class="hljs-built_in">Date</span>.parse(newDatetime))
  timestamp = timestamp.getTime()
  timestamp /= <span class="hljs-number">1000</span>

  <span class="hljs-comment">// 增加8个小时，北京时间比utc时间多八个时区</span>
  timestamp += <span class="hljs-number">8</span> * <span class="hljs-number">60</span> * <span class="hljs-number">60</span>

  <span class="hljs-comment">// 时间戳转为时间</span>
  <span class="hljs-keyword">const</span> beijingDatetime = <span class="hljs-keyword">new</span> <span class="hljs-built_in">Date</span>(<span class="hljs-built_in">parseInt</span>(timestamp, <span class="hljs-number">10</span>) * <span class="hljs-number">1000</span>)
  <span class="hljs-keyword">return</span> beijingDatetime <span class="hljs-comment">// 2017-03-31 16:02:06</span>
}
</div></code></pre>

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